The key phrase here is "I still had domain expertise". Many miss that AI is a multiplier. If you multiply 0 by AI, you get 0 (or hallucinated garbage). You multiplied your knowledge of compound interest and UX by AI's speed. Without your background, the AI would have generated a beautiful interface that calculates mortgages using a savings account formula. Your role shifted from "code writer" to "logic validator" - this is the future of development for domain specialists